A webcam on the PXI now points to a thermometer display showing the tmperature somewhere on the telescope and somewhere in the dome. When the heaters are turned on the telescope readout cycles between about 16 degrees C and more than 60 C.
We presume that the temperature is telling us something about an area near one of the two shutters. Since the shutter shows the sticking behaviour through these temperature cycles the sticking problem is either unrelated to the temperature of the shutter or the temperature we can see is not from an area close to the shutter inside the telescope.
We think that the sticking shutter is the one inside the telescope because the system that reads the shutter time also indicates failure whenever a picture is ‘bias like’, which would not be the case if the failing shutter was the front barrel one.